Strike-Slip in Cold – Summary of the Disaster Happening In Turkey

On the morning of February 6th, the nation awoke to devastating news: a 7.8-magnitude earthquake had struck the Southeast region of Turkey at 04:17 a.m. Tremors were felt in numerous cities, including the capital, Ankara. Reports soon confirmed the collapse of buildings in ten regional cities, and the race against time began.

Technical Details

The moment magnitude of the mainshock was determined as 7.7 by local stations at an epicenter depth of 8.6 km. This earthquake had particularly high spectral acceleration values. Earthquake engineers Prof. Dr. Oguz Cem Celik, and Dr. Kurtulus Atasever, calculated spectral accelerations obtained from initial data and plotted them against code-based spectra.

“The figures indicate that most of the current building inventory has undergone greater acceleration than their intended design spectra”, stated Dr. Atasever.

The earthquake’s epicenter is situated at the intersection of the Anatolia, Arabian, and African tectonic plates. The United States Geological Survey affirms that the effects of earthquakes extend beyond the point at which they are mapped. For example, a magnitude 7.5 strike-slip earthquake can rupture a fault line up to 120 kilometers in length and 18 kilometers in width.

After the initial mainshock, seismic activity in the region has been persistent, with over 300 aftershocks recorded within the first three days. Nine hours afterward, another large earthquake of magnitude 7.6 struck Elbistan, Kahramanmaras, at an approximate depth of 7 km. To date, more than 2,400 aftershocks have been reported.

Based on the comments of experts from around the globe on the recent earthquakes, this event is one of the most significant seismic tremors to affect the region in over 500 years. Initial observations indicated that the leading causes of this tragedy are high peak ground acceleration and spectral acceleration exceeding the anticipated design values and structural irregularities. However, it is another fact that several buildings are still standing on the same sites as the collapsed ones. This brings us to a question. Could this tragedy have been prevented? Was it possible to prevent these buildings from total collapse?

This tragedy highlighted the importance of urbanization based on scientific principles, safe and reliable construction, and adequate supervision. Examples of buildings that withstood strong ground motions include those designed by the experts of Prota Engineering. These buildings shared the common features of designing and retrofitting in compliance with the Turkish Seismic Regulations for both new and existing structures. Particularly, the utilization of seismic isolation systems in hospital buildings has provided effective energy dissipation, reducted spectral accelerations acting on the upper structure, and limited interstorey drifts. Depending on the performance expected from the buildings, a proper design and retrofit may not prevent damage but definitely prevent total or partial collapse even during maximum considered earthquakes, providing life safety. Nonetheless, all buildings must be able to guarantee life safety and collapse prevention.

Some buildings of Iskenderun State Hospital collapsed during the mainshocks. It was clearly an unacceptable seismic performance from a hospital building. Hospitals are essential structures and should be built to be operational within serviceability limits due to life-critical medical devices and services, even after destructive ground motions.

Prota Engineering has designed 15 hospitals with base isolation in high seismic regions of Turkey so far, three of which are located in this region. Elbistan State Hospital and Malatya Maternity and Children Hospital, located in the center of these earthquakes, survived with no damage and are operational now. The 3rd hospital was still under construction in Adıyaman, and no damage was observed.

There are two seismic isolation layers in Elbistan State Hospital, which has 48,000 sq meters of closed space. The primary isolation layer is at the top of the bottom storey columns, while the second isolation layer is located at the bottom of the shear walls. Both upper and lower structure design was performed using the ProtaStructure software equipped with state-of-the-art seismic design capabilities developed by Prota Software.

Malatya Maternity and Children Hospital was also designed using seismic isolation systems to guarantee the operational conditions following the ground motions even exceeding the design earthquake level. This hospital, designed using the ProtaStructure software, has protected its 300-bed capacity from catastrophic damage. This hospital is now crucial for providing immediate medical care to those affected in the region.